Combustion Of Coal Blends Research Articles

Combustion and Self-Desulfurization Characterization of Blended Low-Rank Coals for Improved Resource Utilization in Fluidized Bed Boilers

Combustion and Self-Desulfurization Characterization of Blended Low-Rank Coals for Improved Resource Utilization in Fluidized Bed Boilers

Experimental investigation on the effect of blending bituminous coal with pinus sawdust on combustion performance parameters

Combustion of bituminous coal and pinus sawdust blends was investigated experimentally within a drop tube furnace (DTF) with the aim of determining particle residence times and temperatures during the process. Evaluation of these parameters gives useful information to engineers who want to optimise the co-combustion process of coal and biomass blends. The DTF experimental approach was used to investigate fuel blends with a pinus sawdust mass substitution of 0, 10, 20, and 30% at different furnace temperatures of 1273, 1473 and 1673 K. Results showed that during stage 1 of the experimental setup which mimics devolatilisation, particle residence time at a distance of 520 mm from the injection point decreased from 0.8 to 0.7 s as blending by pinus sawdust increased from 0 to 30 %. During stage 2 of the experimental setup which mimics char combustion, particle residence time at a distance of 1320 mm from the injection point decreased from 3.9 to 2.0 s as blending by pinus sawdust increased from 0 to 30 %. The blending ratios under investigation demonstrated similar profiles of particle temperature at different furnace positions though further analysis showed that the highly blended samples required less time to attain high temperatures. By extension, since fuel blends with higher percentages of pinus sawdust were able to attain higher temperatures at shorter residence time, combustion intensity was deduced to increase with the blending ratio whilst stability decreased. As such, caution should be taken with materials used for furnace and burner design as high-temperature zones move backwards towards the injection point as blending increases.

Numerical Simulation of Hydrogen–Coal Blending Combustion in a 660 MW Tangential Boiler

With the adjustment of energy structure, the utilization of hydrogen energy has been widely attended. China’s carbon neutrality targets make it urgent to change traditional coal-fired power generation. The paper investigates the combustion of pulverized coal blended with hydrogen to reduce carbon emissions. In terms of calorific value, the pulverized coal combustion with hydrogen at 1%, 5%, and 10% blending ratios is investigated. The results show that there is a significant reduction in CO2 concentration after hydrogen blending. The CO2 concentration (mole fraction) decreased from 15.6% to 13.6% for the 10% hydrogen blending condition compared to the non-hydrogen blending condition. The rapid combustion of hydrogen produces large amounts of heat in a short period, which helps the ignition of pulverized coal. However, as the proportion of hydrogen blending increases, the production of large amounts of H2O gives an overall lower temperature. On the other hand, the temperature distribution is more uniform. The concentrations of O2 and CO in the upper part of the furnace increased. The current air distribution pattern cannot satisfy the adequate combustion of the fuel after hydrogen blending.

Migration and transformation of Pb, Cu, and Zn during co-combustion of high-chlorine-alkaline coal and Si/Al dominated coal

Shaerhu (SEH) coal is abundant in Xinjiang, China. The utilization of SEH suffers from severe ash deposition, slagging, and fouling problems due to its high-chlorine-alkaline characteristics. The co-combustion of high-alkaline coal and other type coals containing high Si/Al oxides has been proven to be a simple and effective method that will alleviate ash-related problems, but the risk of heavy metals (HMs) contamination in this process is nonnegligible. Hence, the volatilization rates and chemical speciation of Pb, Cu, and Zn in co-combusting SEH and a high Si/Al oxides coal, i.e., Yuanbaoshan (YBS) coal were investigated in this study. The results showed that the addition of SEH increased the volatilization rates of Pb, Cu, and Zn during the co-combustion at 800°C from 23.70%, 23.97%, and 34.98% to 82.31%, 30.01%, and 44.03%, respectively, and promoted the extractable state of Cu and Zn. In addition, the interaction between SEH and YBS inhibited the formation of the Pb residue state. SEM-EDS mapping results showed that compared to Zn and Cu, the signal intensity of Pb was extremely weak in regions where some of the Si and Al signal distributions overlap. The DFT results indicated that the O atoms of the metakaolin (Al2O3⋅2SiO2) (001) surface were better bound to the Zn and Cu than Pb atoms after adsorption of the chlorinated HMs. These results contribute to a better understanding of the effects of high-alkaline coal blending combustion on Pb, Cu, and Zn migration and transformation.

Insight into the combustion effect of the high-reactivity char particle on the low-reactivity char particle in a hot O2/CO2 atmosphere

Based on the pseudo-steady-state approach, the combustion effect of high-reactivity char (i.e., HR-char) on low-reactivity char (i.e., LR-char) is investigated numerically in a hot O2/CO2 atmosphere under two arrangements (LR-LR case: the upstream and downstream particles are LR-char, HR-LR case: the upstream particle is HR-char and the downstream particle is LR-char). This paper is aimed to study the influence of oxygen concentration (from 2% to 30%) and ambient temperature (1300 K, 1400 K, and 1500 K) on the combustion effect under the condition with dominated oxidation reaction and weak gasification reaction, and explain the mechanism in aspects of the temperature, specie concentration, and reaction rate. The numerical results are carefully validated against experimental data published in the literature. The results show that under these studied ambient temperatures, the char-O2 oxidation-reduction brings a more pronounced effect than the char-CO2 gasification enhancement for char consumption owning to the dominant role of the char oxidation reaction. The upstream HR-char particle combustion under the HR-LR case produces a higher temperature, lower oxygen, and higher CO2 atmosphere ahead of the downstream char than under the LR-LR case, which significantly inhibits the downstream LR-char particle combustion. In addition, lower oxygen concentration or higher ambient temperature decreases the difference in temperature, oxygen, and CO2 between the HR-LR and LR-LR cases ahead of the downstream char, resulting in the lower difference in the downstream LR-char oxidation consumption rate between the HR-LR and LR-LR case. Consequently, the weaker combustion inhibitive effect of the high-reactivity char on the low-reactivity char is observed. The findings shed light on the interaction effects observed during blended coal combustion in O2/CO2 mixtures.

Combustion Interactions of Blended Chars under Oxidation and Gasification Competition in Oxy–Fuel Condition

The combustion interactions during blended coal combustion affect their combustion characteristics, and the combustion interactions under air–fuel conditions have been well studied. However, oxy–fuel combustion considerably differs from air–fuel firing. Significantly, the char–CO2 gasification reaction under oxy–fuel and high-temperature conditions substantially affects the combustion behaviors, which may influence the combustion interactions. This paper is to study the effect of the char oxidation and gasification reaction competition on comprehensive interactions in O2/CO2 mixture. The results show that under high-temperature and low-oxygen (O2<4%) conditions, an intense gasification reaction is observed. The competition between the char–CO2 gasification and char–O2 oxidation reactions influences the comprehensive interactions during blended chars combustion. As the char–O2 oxidation reaction is strengthened and the char–CO2 gasification reaction is weakened, the comprehensive interactions during blended chars combustion gradually decrease. Moreover, under the competition between the char–CO2 gasification and char–O2 oxidation reactions, only enhancing the char–CO2 gasification reaction or enhancing the char–O2 oxidation reaction weakens the comprehensive interactions. The weaker comprehensive interactions result in the smaller nonadditive behavior of the comprehensive combustion index. The findings shed light on the interaction effects observed during blended chars combustion, which can provide useful information to improve the combustion behaviors of the blended coals in oxy–fuel conditions.

Determining the optimum fuel concentration for ignition and combustion of semi-coke and bituminous coal blends with rich/lean burner

To burn semi-coke with ultra-low volatile content effectively at a large blending proportion with high volatile bituminous coal using a pulverized fuel (PF) rich/lean burner, the ignition and combustion behaviors of blended fuel of semi-coke and bituminous coal (1:1 by weight) in reducing to oxidizing atmosphere were investigated in a 300 kW pilot-scale test furnace with an arrangement of varying pulverized fuel-rich side stream concentration (Pfc,rich, kg/kg). The results showed that ignition distance of the fuel-rich stream decreased from 339 mm to 159 mm when Pfc,rich increased from 0.37 kg/kg to 0.58 kg/kg, which then increased again to 0.63 kg/kg. The ignition distance for the fuel-lean stream increased monotonically from 332 mm to 383 mm with an increase in the Pfc,rich. The intersection of two streams showed a positive effect on overall ignition when Pfc,rich was varied from 0.49 kg/kg to 0.58 kg/kg, which was mainly attributed to the mean volatile content of blended fuel. A parameter Vindex was introduced to evaluate the effects of quantity of volatiles on the ignition behaviour of blended fuels, and it was found that the volatile effect was more sensitive to the ignition distance than the ignition temperature. The ignition of the fuel-rich stream transformed from the heterogeneous-homogeneous combined mode to the homogeneous mode at Pfc,rich of 0.49 kg/kg. The burnout ratio of blended fuel was highest at Pfc,rich = 0.52 kg/kg and 12.21% higher than that of the ordinary unbiased burner. NO emission was inhibited under rich/lean combustion conditions, and the existence of a strong reducing zone was the key factor for the low conversion ratio of fuel-N to NO. Based on the experimental results, Pfc,rich ranging from 0.52 kg/kg to 0.58 kg/kg was observed to be optimum for rich/lean co-combustion at large proportion of semi-coke in the blends.

Ilmenite as alternative bed material for the combustion of coal and biomass blends in a fluidised bed combustor to improve combustion performance and reduce agglomeration tendency

Co-firing coal and biomass has the potential to reduce GHG emissions. However, high levels of alkali and alkaline metals in biomass ash can bring additional issues to the operation of coal-fired boilers. This study investigates the effects of ilmenite as the bed material on CO and NOx emissions and combustion efficiency of a coal and biomass blend, and the agglomeration tendency of the bed material with a pilot-scale (30 kWth) bubbling fluidised bed combustor. The experiments were carried out at 900 °C using a bituminous coal blended with wheat straw pellets at 40 wt% as the fuel and silica sand as the baseline bed material. Samples of agglomerates collected from the combustor and cyclone ash were characterised by SEM-EDS, XRD, and XRF. The results revealed that ilmenite could reduce the level of excess air required to achieve complete combustion due to lower CO emissions and less efficiency loss compared to silica sand. However, ilmenite increased NOx emissions. Furthermore, the characterisation of the obtained agglomerates and cyclone ash showed that ilmenite could hinder the K-rich molten substance attachment to the bed material, leading to significantly smaller agglomerates and hence less tendency towards defluidisation in comparison to silica sand.

Experimental investigation for the combustion characteristics of blends of three kinds of coal

The uneven distribution of coal resources coupled with changes in coal market prices in China have led many power plants to adopt blended coal combustion technology. Because of the varying combustion characteristics of the blended coals, it is necessary to study the combustion characteristics of the blended coals. In this study, blended coal were produced between the bituminous coals, Nanning meager-lean coals and petroleum coke, according to the mass percentages and particle size combination. A thermogravimetric analyzer is used to investigate the combustion characteristics and kinetic parameters of blended coals of three raw coals under different conditions. The experimental results show that the thermogravimetric curves of the blended coals with different blending ratios are between the thermogravimetric curves of bituminous coal and petroleum coke. Additionally, the blended coal with petroleum coke content at 30% has the optimal combustion performance, but the combustion characteristics of the blended coals deteriorate drastically when the percentage of petroleum coke in the blended coal increases to more than 30%. Kinetic analysis indicates that the activation energy of the stage before 500 °C is higher than that of the stage after 500 °C. As the oxygen concentration increases, nevertheless the mean activation energy of the sample is increased. Besides, the mean activation energy of blended coals shows that the combustion characteristics of blended coals cannot be determined solely by the activation energy derived from the Coats-Redfern method.

Combustion experimental analysis into effects of interaction between blended coals on the NO emission

In studies of blended coal combustion, blending methods have an effect on NO emissions, but few experimental studies investigate the coal combustion in different height of furnace. In order to compare the effects of different blending methods on the NO emission during combustion process, bituminous coal, anthracite and their blended coal were burned in various modes in a two-layer and layer distance adjustable reactor. The results showed that NO emission of blended coal decreased nonlinearly with the blending ratio of bituminous coal (BBR) increasing. It indicated that interactions between component coals affected NO formation, leading to different NO emission in these three blending methods (two in-furnace blending methods and one out-furnace blending method). Compared with other methods, the in-furnace blending method (bituminous coal on the upper layer and anthracite on the lower layer) showed a great potential to reduce NO emission. Particularly, when the layer distance increased to 200 mm and the BBR is 70%, the NO emission reached the lowest.

Computational modeling of flow field in boiler before and after urea injection under different conditions

In order to achieve ultra-low NOx emissions, the effects of total excess air coefficient, air coefficient in main combustion zone, blended-coal combustion, and ammonia-nitrogen molar ratio on a 330 MW coal-fired boiler combustion were studied by numerical simulation. The results show that the velocity field and temperature field in the furnace have synergy, the better the synergy is, the faster the temperature rises, and the more NOx it generates. Compared before and after urea spraying, the NOx concentration decreased with the decrease of the total excess air coefficient, the optimum total excess air coefficient is about 1.15, and the denitrification rate is as high as 76.2%. The smaller the air coefficient in the main combustion zone is, the smaller the NOx concentration is. The optimum air coefficient in the main combustion zone is about 0.92, and the denitrification rate is 85%. After urea injection, the denitrification rate of high volatile coal combustion is higher than that of low volatile coal combustion, and the reasonable blending mode of coal can reduce NOx emissions. The larger the ammonia-nitrogen molar ratio is, the lower the NOx concentration is. When the ammonia-nitrogen molar ratio is greater than 2, the amount of ammonia escape at the flue outlet exceeds the standard. When the ammonia-nitrogen molar ratio is less than 1, the NOx concentration at the flue outlet is greater than that before urea injection. The optimal ammonia-nitrogen molar ratio is about 2.

An Experimental Study on Oxidized Mercury Adsorption by Bromide Blended Coal Combustion Fly Ash

The application of forced mercury oxidation technology would lead to an increase of Hg2+ concentration in the flue gas. Although Hg2+ can be easily removed in the WFGD, the mercury re-emission in the WFGD can decrease the total removal of mercury from coal-fired power plants. Hence, it is necessary to control Hg2+ concentration in the devices before the WFGD. Fly ash adsorbent is considered as a potential alternative for commercial activated carbon adsorbent. However, the adsorption efficiency of the original fly ash is low. Modification procedure is needed to enhance the adsorption performance. In this study, the adsorption of Hg2+ by brominated fly ash was studied. The fly ash was collected from the full-scale power plant utilizing bromide-blended coal combustion technology. The brominated fly ash exhibited excellent performance for Hg2+ removal. The flue gas component HBr and SO2 could improve adsorbent’s performance, while HCl would hinder its adsorption process. Also, it was demonstrated by Hg-TPD experiments that the adsorbed Hg2+ mainly existed on the fly ash surface in the form of HgBr2. In summary, the brominated fly ash has a broad application prospect for mercury control.

In-situ reaction between arsenic/selenium and minerals in fly ash at high temperature during blended coal combustion

Blended coal combustion technology was extensively used in coal-fired power plants in China. In order to investigate the in-situ reaction between trace elements and minerals in fly ash during blended coal combustion, a bituminous (HLH), anthracite (ZW) and the blended coal of these two parent coals were combusted in a drop tube furnace at 1150°C. The ash gathered at high temperature segment (HTA) and low temperature segment (LTA) of the furnace were analyzed, respectively. The results indicated that the retention rates of arsenic in HTA were lower than that in LTA, which suggested that arsenic would be re-absorbed by ash during cooling down of flue gas. For HTA the retention rates of arsenic in ash of ZW, Z3H1, Z1H1, Z1H3, HLH were 60.31%, 26.85%, 13.29%, 20.23% and 36.11%, respectively. The arsenic was more difficult to be captured by HTA of blended coal than that of parent coal. As for selenium, the retention rates in HTA of five coal samples were 24.68%, 23.60%, 20.58%, 15.19% and 38.13%, which had the same retention law as arsenic. The results of X-ray diffraction (XRD) demonstrated that the mineral morphology was changed obviously during blended coal combustion. Unlike parent coal, mullite appeared in HTA of blended coal, and peak of mullite was enhanced with proportion of ZW increased in blended coal. It was consistent with the trend of retention of As and Se in HTA. It illustrated that change of mineral species and in-situ reaction between minerals and trace elements significantly affected emission of arsenic and selenium during blended coal combustion.

Study on the Law of the Influence on Slag Blocking in Combustors Produced by Coal Blending Combustion Strategy of Slag-tap Boiler

Slag blocking and slagging of combustors are influenced by the coal blending combustion strategy of slag-tap boiler. this paper studies these influence factors, analyzes the problems of slag blocking and slagging of combustors from the perspective of fuel, and examines the calorific value, ash content, ash melting point, ash melting characteristics of coal quality and slag captured rate of boiler. Based on the above researches, the writer summarizes the effects on slag blocking and slagging in the combustors produced by different coal combustion of slag-tap boiler, and forms coal blending combustion strategy suitable for the slag-tap boiler.

Combustion interactions in oxy-fuel firing of coal blends: An experimental and numerical study

Coal blends are commonly used in thermal power plants and oxy-fuel combustion also attracts great concerns recently. However, little has been done on oxy-fuel combustion of coal blends. In this paper, combustion tests are performed in a drop tube furnace for various coal blends under O2/CO2 mixtures, which are also reproduced numerically. Strong combustion interactions between the parent coals in a blend are observed. The ignition of the low-volatile coal is promoted due to the rapid combustion of the volatiles from the high-volatile coal. However, the char burnout of the low-volatile coal is compromised due to the rapid O2 consumption by the large amount of volatiles. The interactions under oxy-fuel conditions are more sensitive to the excess O2, inlet oxidizer temperature and coal particle size. 1) The increase in the excess O2 tends to weaken the combustion interactions, in which both the ignition promotion and burnout inhibition effects on the low-volatile coal become less apparent. 2) The increase in the inlet oxidizer temperature further promotes the ignition of the low-volatile coal whereas weakens the burnout inhibition of the low-volatile coal. 3) The effects of reducing particle size on the combustion interactions are similar to those of increasing inlet oxidizer temperature. Since biomass often contains a high volatile content, the findings may shed light on the synergistic effects in oxy-fuel co-combustion of biomass and coal.

Effect of H2O on the combustion characteristics and interactions of blended coals in O2/H2O/CO2 atmosphere

Blending coal combustion technology is commonly used in coal-fired power stations, and the combustion interactions (i.e., the ignition promotion and burnout inhibition) during blended coal combustion affect their combustion characteristics. The combustion interactions under conventional air-fuel condition have been well studied. Oxy-fuel firing considerably differs from air-fuel combustion and the combustion interactions of blended coals in O2/CO2 atmospheres have been investigated in our previous research. However, the H2O concentration in actual oxy-fuel condition is relatively high, which may influence the combustion interactions. This study further investigates the effect of H2O on the combustion characteristics and interactions of blended coals in O2/H2O/CO2 atmospheres. The results show that adding H2O into the oxy-fuel atmosphere remarkably affects the combustion characteristics with the more notable ignition delay, faster burnout and better comprehensive combustion characteristics (CCI). In addition, the presence of H2O strengthens the ignition promotion, the burnout inhibition and the comprehensive interactions, resulting in the more obvious non-additive behaviors of CCI. In O2/H2O/CO2 mixtures, enhancing the H2O/CO2 ratio slightly strengthens the ignition promotion, the burnout inhibition, and the comprehensive interactions, which increases the non-additive behaviors of CCI. Furthermore, both of increasing O2/H2O or O2/CO2 ratios significantly weaken the ignition promotion, strengthen the burnout inhibition and the comprehensive interactions, which increases the non-additive behaviors of CCI. The findings shed light on the interaction effects observed during blended coal combustion in O2/H2O/CO2 mixtures, which can provide useful information to improve the combustion characteristics of the blended coals in the real oxy-fuel atmospheres.

Effect of coaxial oxygen enrichment on three different coals and their blends

ABSTRACT Mathematical models appear as very attractive alternatives in blast furnace studies. Therefore, a three-dimensional model is described and validated to simulate the flow and combustion of binary coal blends under simplified blast furnace conditions. The present article aims to analyse the performance of different coals and their blends for conventional and coaxial oxygen enrichment methods. Among the simulated coals, Coal C, which combines one of the smallest particle sizes with one of the highest volatile matter contents, presented the highest burnout and average temperature values. Coaxial oxygen enrichment showed a negative effect on coal combustibility in the cases with 26.9% of O2. This is explained by the large amount of gas being injected by the coaxial lance, resulting in a cooling effect and particle concentration. Also, blending coal A with coal B resulted in an improvement of burnout for both coals, because of the synergetic effect caused by their combustion.

NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals

Low NOx combustion of blended coals is widely used in coal-fired boilers in China to control NOx emission; thus, it is necessary to understand the formation mechanism of NOx and H2S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NOx and H2S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H2S, and NOx in the fuelrich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H2S as NO reduction accelerated. Both the CO and H2S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H2S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus, CO, NOx, and H2S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.

Laboratorijskim istraživanjem do izbora mjesta uvođenja stepenovanog vazduha za sagorijevanje u ložište

In general, the mixing the reactants is very important to the process and the rate of combustion of each fuel, especially low-ranked coals with low reactivity. The appropriate excess air coefficient for combustion and the position and mode of supply of individual portions (air sta- ging) of the total air in the furnace are one of the key influ- encing factors for the mixing, respectively the efficiency of the combustion process, and the level of emissions. Today, the air staging (primary, secondary, tertiary and over fire air-OFA) is an indispensable process in the design of new industrial and energy boilers. Also, this measures are used for the reconstru- ction of existing furnace of large boilers. The implementation of this primary measure in the furnace does not require signi- ficant financial resources - the costs of investing in the intro- duction of air staging supply for combustion in the furnace are very low in relation to the multiple positive effects and bene- fits of such a system, especially a lower NOx emissions. However, the first condition for the correct and reliable design of the air staging system in the furnace is the choice of the optimal position for the supply OFA air. Determination of this position on the furnace depends on several factors, primarily the type and characteristics of the fuel, grinding quality, co- mbustion technology, furnace structure, type, number and arra- ngement of burners. On this topic, the Faculty of Mechanical Engineering of the University of Sarajevo, in the Laboratory for Coal and Biomass Combustion, conducted extensive rese- arch on the pulverized combustion of coal blends of the Ce- ntral Bosnia Mining Basin, including co-firing of these coals with waste wood biomass (beech and spruce sawdust). Here is presented some of the results of those NOx emission studies for different fuels and combustion temperatures, depending on the mode of supply and the positions of the combustion air supply in the boiler furnace.

Stochastic Economic Dispatch of Hydro-Thermal-Wind-Photovoltaic Power System Considering Mixed Coal-Blending Combustion

This paper proposes a stochastic economic dispatch (SED) model for hydro-thermal-wind-photovoltaic power system (HTWPPS) considering mixed coal-blending combustion (MCBC) to improve the operational efficiencies of thermal power units (TPUs) with deep peak-regulating operation (DPRO). Firstly, the rations for different types of coal can be acquired by meeting the operational requirements of boilers. Three functions including the cost of coal consumption, polluting gas emission, and the life loss cost for TPUs could be obtained by fitting coal quality. Besides, they would be strictly piecewise linearized, respectively. Consequently, the objective function involving the above three kinds of costs as well as the cost of oil injection can be presented. Secondly, there is a two-stage framework for reducing the coupling of HTWPPS and improving the solving efficiency. In the first stage, the Monarch Butterfly Optimization (MBO) algorithm is employed for obtaining the power outputs of hydro-power units (HPUs) taking the minimum water consumption as the objective. In the second stage, the load curve can be updated according to the results from the first stage. Besides, the Latin Hypercube Sampling method and the backward scene reduction technique are utilized to acquire a set of scenarios of wind power. In this way, the SED model considering MCBC can be achieved. The case studies have been carried out on a simplified provincial power system in China with the help of MATPOWER and CPLEX. The results show that the proposed model can effectively increase the economic and environmental benefits for TPUs.